Three-piece infrared single wavelength lens system

ABSTRACT

A three-piece infrared single wavelength lens system includes, in order from the object side to the image side: a stop, a first lens element with a positive refractive power, a second lens element with a positive refractive power, and a third lens element with a positive refractive power. The focal length of the first lens element is f1, the focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.5&lt;f1/f23&lt;1.0. When the above relation is satisfied, a wide field of view can be obtained and the resolution can be improved evidently.

BACKGROUND

Field of the Invention

The present invention relates to a lens system, and more particularly toa miniaturized three-piece infrared single wavelength lens systemapplicable to electronic products.

Description of the Prior Art

Nowadays digital imaging technology is constantly innovating andchanging, in particular, digital carriers, such as, digital camera andmobile phone and so on, have become smaller in size, so CCD (ChargeCoupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensoris also required to be more compact. In addition to be used in the fieldof photography, in recent years, infrared focusing lens has also be usedin infrared receiving and sensing field of the game machine, and inorder to make the scope of game machine induction user more broader,wide-angle lens group has become the mainstream for receiving infraredwavelength at present.

The applicant has also put forward a number of lens groups related toinfrared wavelength reception, such as the single focus wide-angle lensmodules disclosed in TW Appl. Nos. 098100552, 098125378 and U.S. Pat.Nos. 8,031,413, 8,369,031, however, at present, the game machine isbased on a more three-dimensional, real and immediate 3D game, thecurrent or the applicant's previous lens groups are all 2D plane games,which cannot meet the 3D game focusing on the deep induction efficacy.

Special infrared receiving and induction lens groups for game machinesare made of plastic for the pursuit of low cost, however, poor materialtransparency is one of the key factors that affect the depth detectionaccuracy of the game machine, and plastic lenses are easy to overheat ortoo cold in ambient temperature, so that the focal length of the lensgroup will be changed and cannot focus accurately. Therefore, thecurrent infrared receiving and induction lens groups cannot meet the 3Dgame depth precise induction requirement.

The present invention mitigates and/or obviates the aforementioneddisadvantages.

SUMMARY OF THE INVENTION

The present invention is aimed at providing a three-piece infraredsingle wavelength lens system with better image sensing function.

Therefore, a three-piece infrared single wavelength lens system inaccordance with the present invention comprises, in order from an objectside to an image side: a stop; a first lens element with a positiverefractive power, having an object-side surface being convex near anoptical axis and an image-side surface being convex near the opticalaxis, at least one of the object-side surface and the image-side surfaceof the first lens element being aspheric; a second lens element with apositive refractive power, having an object-side surface being concavenear the optical axis and an image-side surface being convex near theoptical axis, at least one of the object-side surface and the image-sidesurface of the second lens element being aspheric; and a third lenselement with a positive refractive power having an object-side surfacebeing convex near the optical axis and an image-side surface beingconcave near the optical axis, at least one of the object-side surfaceand the image-side surface of the third lens element being aspheric.

A focal length of the first lens element is f1, a focal length of thesecond lens element and the third lens element combined is f23, and theysatisfy the relation: 0.5<f1/f23<1.0, so that a wide field of view canbe obtained and the resolution can be improved evidently.

Preferably, the focal length of the first lens element is f1, a focallength of the second lens element is f2, and they satisfy the relation:0.05<f1/f2<0.45, so that the refractive power of the first lens elementand the second lens element are more suitable, it will be favorable toobtain a wide field of view and avoid the excessive increase ofaberration of the system.

Preferably, the focal length of the second lens element is f2, a focallength of the third lens element is f3, and they satisfy the relation:0.5<f2/f3<2.6, so that the refractive power of the second lens elementand the third lens element are more balanced, it will be favorable tocorrect the aberration of the system and reduce the sensitivity of thesystem.

Preferably, the focal length of the first lens element is f1, the focallength of the third lens element is f3, and they satisfy the relation:0.05<f1/f3<0.7, so that the positive refractive power of the first lenselement can be distributed effectively, so as to reduce the sensitivityof the three-piece infrared single wavelength lens system.

Preferably, a focal length of the first lens element and the second lenselement combined is f12, the focal length of the third lens element isf3, and they satisfy the relation: 0.1<f12/f3<0.65, so that a wide fieldof view can be obtained and the resolution can be improved evidently.

Preferably, a radius of curvature of the image-side surface of the firstlens element is R2, a radius of curvature of the object-side surface ofthe second lens element is R3, and they satisfy the relation:25<R2/R3<270, which can reduce the spherical aberration and astigmatismof the three-piece infrared single wavelength lens system.

Preferably, the three-piece infrared single wavelength lens system has amaximum view angle FOV, and it satisfies the relation: 45<FOV<75, sothat the three-piece infrared single wavelength lens system will have anappropriately large field of view.

Preferably, a central thickness of the first lens element along theoptical axis is CT1, a distance along the optical axis between the firstlens element and the second lens element is T12, and they satisfy therelation: 1.4<CT1/T12<2.4, which is favorable to the assembly of thelens group, improving the yield of production.

Preferably, the distance along the optical axis between the first lenselement and the second lens element is T12, a central thickness of thesecond lens element along the optical axis is CT2, and they satisfy therelation: 0.5<T12/CT2<1.4, which is favorable to the formation andhomogeneity of lenses and can increase the yield of assembly.

Preferably, the distance along the optical axis between the first lenselement and the second lens element is T12, a distance along the opticalaxis between the second lens element and the third lens element is T23,and they satisfy the relation: 5.4<T12/T23<9.0, so that the distancebetween the lens elements is more suitable, it will be favorable to theassembly of the lenses, increasing the yield of finished products.

Preferably, an Abbe number of the first lens element is V1, an Abbenumber of the second lens element is V2, and they satisfy the relation:30<V1−V2<42, which can reduce the spherical aberration and astigmatismof the three-piece infrared single wavelength lens system effectively.

Preferably, the Abbe number of the first lens element is V1, an Abbenumber of the third lens element is V3, and they satisfy the relation:30<V1−V3<42, so that the chromatic aberration of the three-pieceinfrared single wavelength lens system can be modified effectively,improving the image quality.

Preferably, a f-number of the three-piece infrared single wavelengthlens system is Fno, and it satisfies the relation: 1.2<Fno<1.8, so thatthe size of the stop of the three-piece infrared single wavelength lenssystem can be adjusted properly, making the three-piece infrared singlewavelength lens system has a big stop.

The present invention will be presented in further details from thefollowing descriptions with the accompanying drawings, which show, forpurpose of illustrations only, the preferred embodiments in accordancewith the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a three-piece infrared single wavelength lens system inaccordance with a first embodiment of the present invention;

FIG. 1B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the first embodimentof the present invention;

FIG. 2A shows a three-piece infrared single wavelength lens system inaccordance with a second embodiment of the present invention;

FIG. 2B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the second embodimentof the present invention;

FIG. 3A shows a three-piece infrared single wavelength lens system inaccordance with a third embodiment of the present invention;

FIG. 3B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the third embodimentof the present invention;

FIG. 4A shows a three-piece infrared single wavelength lens system inaccordance with a fourth embodiment of the present invention; and

FIG. 4B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the fourth embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1A and 1B, FIG. 1A shows a three-piece infraredsingle wavelength lens system in accordance with a first embodiment ofthe present invention, and FIG. 1B shows, in order from left to right,the longitudinal spherical aberration curves, the astigmatic fieldcurves, and the distortion curve of the first embodiment of the presentinvention. A three-piece infrared single wavelength lens system inaccordance with the first embodiment of the present invention comprisesa stop 100 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 110, a second lenselement 120, a third lens element 130, an IR cut filter 170, and animage plane 180, wherein the three-piece infrared single wavelength lenssystem has a total of three lens elements with refractive power. Thestop 100 is disposed between an image-side surface 112 of the first lenselement 110 and an object to be imaged.

The first lens element 110 with a positive refractive power has anobject-side surface 111 being convex near an optical axis 190 and theimage-side surface 112 being convex near the optical axis 190, theobject-side surface 111 and the image-side surface 112 are aspheric, andthe first lens element 110 is made of plastic material.

The second lens element 120 with a positive refractive power has anobject-side surface 121 being concave near the optical axis 190 and animage-side surface 122 being convex near the optical axis 190, theobject-side surface 121 and the image-side surface 122 are aspheric, andthe second lens element 120 is made of plastic material.

The third lens element 130 with a positive refractive power has anobject-side surface 131 being convex near the optical axis 190 and animage-side surface 132 being concave near the optical axis 190, theobject-side surface 131 and the image-side surface 132 are aspheric, andthe third lens element 130 is made of plastic material.

The IR cut filter 170 made of glass is located between the third lenselement 130 and the image plane 180 and has no influence on the focallength of the three-piece infrared single wavelength lens system.

The equation for the aspheric surface profiles of the respective lenselements of the first embodiment is expressed as follows:

wherein:

$z = {\frac{{ch}^{2}}{1 + \left\lbrack {1 - {\left( {k + 1} \right)c^{2}h^{2}}} \right\rbrack^{0.5}} + {Ah}^{4} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Gh}^{14} + \ldots}$

z represents the value of a reference position with respect to a vertexof the surface of a lens and a position with a height h along theoptical axis 190;

c represents a paraxial curvature equal to 1/R (R: a paraxial radius ofcurvature);

h represents a vertical distance from the point on the curve of theaspheric surface to the optical axis 190;

k represents the conic constant;

A, B, C, D, E, G, . . . : represent the high-order asphericcoefficients.

In the first embodiment of the present three-piece infrared singlewavelength lens system, a focal length of the three-piece infraredsingle wavelength lens system is f, a f-number of the three-pieceinfrared single wavelength lens system is Fno, the three-piece infraredsingle wavelength lens system has a maximum view angle (field of view)FOV, and they satisfy the relations: f=1.192 mm; Fno=1.4; and FOV=60degrees.

In the first embodiment of the present three-piece infrared singlewavelength lens system, a focal length of the first lens element 110 isf1, a focal length of the second lens element 120 and the third lenselement 130 combined is f23, and they satisfy the relation:f1/f23=0.64636.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, a focal length of the second lens element 120 is f2, and theysatisfy the relation: f1/f2=0.22985.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the focal length of the second lens element 120is f2, a focal length of the third lens element 130 is f3, and theysatisfy the relation: f2/f3=1.39174.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, the focal length of the third lens element 130 is f3, and theysatisfy the relation: f1/f3=0.31990.

In the first embodiment of the present three-piece infrared singlewavelength lens system, a focal length of the first lens element 110 andthe second lens element 120 combined is f12, the focal length of thethird lens element 130 is f3, and they satisfy the relation:f12/f3=0.32798.

In the first embodiment of the present three-piece infrared singlewavelength lens system, a radius of curvature of the image-side surface112 of the first lens element 110 is R2, a radius of curvature of theobject-side surface 121 of the second lens element 120 is R3, and theysatisfy the relation: R2/R3=261.90368.

In the first embodiment of the present three-piece infrared singlewavelength lens system, a central thickness of the first lens element110 along the optical axis 190 is CT1, a distance along the optical axis190 between the first lens element 110 and the second lens element 120is T12, and they satisfy the relation: CT1/T12=1.85473.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the distance along the optical axis 190 betweenthe first lens element 110 and the second lens element 120 is T12, acentral thickness of the second lens element 120 along the optical axis190 is CT2, and they satisfy the relation: T12/CT2=0.97384.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the distance along the optical axis 190 betweenthe first lens element 110 and the second lens element 120 is T12, adistance along the optical axis 190 between the second lens element 120and the third lens element 130 is T23, and they satisfy the relation:T12/T23=7.159.

In the first embodiment of the present three-piece infrared singlewavelength lens system, an Abbe number of the first lens element 110 isV1, an Abbe number of the second lens element 120 is V2, and theysatisfy the relation: V1−V2=34.5.

In the first embodiment of the present three-piece infrared singlewavelength lens system, the Abbe number of the first lens element 110 isV1, an Abbe number of the third lens element 130 is V3, and they satisfythe relation: V1−V3=34.5.

The detailed optical data of the first embodiment is shown in table 1,and the aspheric surface data is shown in table 2.

TABLE 1 Embodiment 1 f(focal length) = 1.192 mm, Fno = 1.4, FOV = 60deg. Curvature surface Radius Thickness Material Index Abbe # Focallength 0 object infinity 500.000 1 infinity 0.002 2 stop infinity −0.0023 Lens 1 0.866 (ASP) 0.398 plastic 1.544 56.000 1.610 4 −107.896 (ASP)0.215 5 Lens 2 −0.412 (ASP) 0.221 plastic 1.651 21.500 7.005 6 −0.454(ASP) 0.030 7 Lens 3 0.658 (ASP) 0.256 plastic 1.651 21.500 5.034 80.707 (ASP) 0.379 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10infinity 0.131 11 Image infinity 0.000 plane

TABLE 2 Aspheric Coefficients surface 3 4 5 K: 1.6561E−01 9.0001E+01−5.0677E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −1.7783E−01−3.8297E−01 2.8597E+00 C: 2.2848E+00 7.7170E+00 −5.9554E+00 D:−5.8170E+01 −1.3481E+02 −6.6323E+01 E: 5.3783E+02 1.0727E+03 1.1671E+03F: −2.3081E+03 −3.8622E+03 −4.7624E+03 G 3.4798E+03 4.9505E+036.3678E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K:−1.5487E+00 −1.1929E+01 −6.9879E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00B: −4.3135E−01 2.0091E+00 −5.2294E−01 C: 5.6008E+00 −2.1131E+011.5078E+00 D: −5.8963E+01 1.1419E+02 −1.1792E+01 E: 3.4446E+02−3.9602E+02 3.2929E+01 F: −7.4388E+02 7.4075E+02 −5.7999E+01 G5.0956E+02 −6.2921E+02 4.4847E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

The units of the radius of curvature, the thickness and the focal lengthin table 1 are expressed in mm, the surface numbers 0-11 represent thesurfaces sequentially arranged from the object-side to the image-sidealong the optical axis. In table 2, k represents the conic coefficientof the equation of the aspheric surface profiles, and A, B, C, D, E, F,G, H . . . : represent the high-order aspheric coefficients. The tablespresented below for each embodiment are the corresponding schematicparameter and aberration curves, and the definitions of the tables arethe same as Table 1 and Table 2 of the first embodiment. Therefore, anexplanation in this regard will not be provided again.

Referring to FIGS. 2A and 2B, FIG. 2A shows a three-piece infraredsingle wavelength lens system in accordance with a second embodiment ofthe present invention, and FIG. 2B shows, in order from left to right,the longitudinal spherical aberration curves, the astigmatic fieldcurves, and the distortion curve of the second embodiment of the presentinvention. A three-piece infrared single wavelength lens system inaccordance with the second embodiment of the present invention comprisesa stop 200 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 210, a second lenselement 220, a third lens element 230, an IR cut filter 270, and animage plane 280, wherein the three-piece infrared single wavelength lenssystem has a total of three lens elements with refractive power. Thestop 200 is disposed between an image-side surface 212 of the first lenselement 210 and an object to be imaged.

The first lens element 210 with a positive refractive power has anobject-side surface 211 being convex near an optical axis 290 and theimage-side surface 212 being convex near the optical axis 290, theobject-side surface 211 and the image-side surface 212 are aspheric, andthe first lens element 210 is made of plastic material.

The second lens element 220 with a positive refractive power has anobject-side surface 221 being concave near the optical axis 290 and animage-side surface 222 being convex near the optical axis 290, theobject-side surface 221 and the image-side surface 222 are aspheric, andthe second lens element 220 is made of plastic material.

The third lens element 230 with a positive refractive power has anobject-side surface 231 being convex near the optical axis 290 and animage-side surface 232 being concave near the optical axis 290, theobject-side surface 231 and the image-side surface 232 are aspheric, andthe third lens element 230 is made of plastic material.

The IR cut filter 270 made of glass is located between the third lenselement 230 and the image plane 280 and has no influence on the focallength of the three-piece infrared single wavelength lens system.

The detailed optical data of the second embodiment is shown in table 3,and the aspheric surface data is shown in table 4.

TABLE 3 Embodiment 2 f(focal length) = 1.264 mm, Fno = 1.4, FOV = 55deg. Curvature surface Radius Thickness Material Index Abbe # Focallength 0 object infinity 500.000 1 infinity 0.003 2 stop infinity −0.0033 Lens 1 0.956 (ASP) 0.479 plastic 1.544 56.000 1.760 4 −56.134 (ASP)0.258 5 Lens 2 −0.453 (ASP) 0.221 plastic 1.651 21.500 9.111 6 −0.499(ASP) 0.030 7 Lens 3 0.669 (ASP) 0.274 plastic 1.651 21.500 4.227 80.752 (ASP) 0.367 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10infinity 0.144 11 Image infinity 0.000 plane

TABLE 4 Aspheric Coefficients surface 3 4 5 K: 1.4591E−01 8.6453E+03−5.0418E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −1.4983E−01−2.5141E−01 2.1650E+00 C: 1.4038E+00 4.8007E+00 −3.7831E+00 D:−2.9628E+01 −6.9229E+01 −3.4353E+01 E: 2.2943E+02 4.5491E+02 4.9418E+02F: −8.0646E+02 −1.3541E+03 −1.6700E+03 G 1.0122E+03 1.4330E+031.8433E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K:−1.4998E+00 −1.0282E+01 −5.4983E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00B: −3.2878E−01 1.8526E+00 −8.3680E−02 C: 3.5347E+00 −1.3143E+011.1134E+00 D: −3.0133E+01 5.8273E+01 −6.4602E+00 E: 1.4609E+02−1.6768E+02 1.3145E+01 F: −2.6120E+02 2.6112E+02 −2.0481E+01 G1.4485E+02 −1.7938E+02 1.5542E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

In the second embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the second embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 3 and Table 4 asthe following values and satisfy the following conditions:

Embodiment 2 f 1.264 f12/f3 0.43356 Fno 1.4 R2/R3 123.96486 FOV 55CT1/T12 1.85478 f1/f2 0.19314 T12/CT2 1.16877 f2/f3 2.15539 T12/T238.60333 f1/f3 0.41629 V1 − V2 34.5 f1/f23 0.71360 V1 − V3 34.5

Referring to FIGS. 3A and 3B, FIG. 3A shows a three-piece infraredsingle wavelength lens system in accordance with a third embodiment ofthe present invention, and FIG. 3B shows, in order from left to right,the longitudinal spherical aberration curves, the astigmatic fieldcurves, and the distortion curve of the third embodiment of the presentinvention. A three-piece infrared single wavelength lens system inaccordance with the third embodiment of the present invention comprisesa stop 300 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 310, a second lenselement 320, a third lens element 330, an IR cut filter 370, and animage plane 380, wherein the three-piece infrared single wavelength lenssystem has a total of three lens elements with refractive power. Thestop 300 is disposed between an image-side surface 312 of the first lenselement 310 and an object to be imaged.

The first lens element 310 with a positive refractive power has anobject-side surface 311 being convex near an optical axis 390 and theimage-side surface 312 being convex near the optical axis 390, theobject-side surface 311 and the image-side surface 312 are aspheric, andthe first lens element 310 is made of plastic material.

The second lens element 320 with a positive refractive power has anobject-side surface 321 being concave near the optical axis 390 and animage-side surface 322 being convex near the optical axis 390, theobject-side surface 321 and the image-side surface 322 are aspheric, andthe second lens element 320 is made of plastic material.

The third lens element 330 with a positive refractive power has anobject-side surface 331 being convex near the optical axis 390 and animage-side surface 332 being concave near the optical axis 390, theobject-side surface 331 and the image-side surface 332 are aspheric, andthe third lens element 330 is made of plastic material.

The IR cut filter 370 made of glass is located between the third lenselement 330 and the image plane 380 and has no influence on the focallength of the three-piece infrared single wavelength lens system.

The detailed optical data of the third embodiment is shown in table 5,and the aspheric surface data is shown in table 6.

TABLE 5 Embodiment 3 f(focal length) = 1.076 mm, Fno = 1.6, FOV = 65deg. Curvature surface Radius Thickness Material Index Abbe # Focallength 0 object infinity 500.000 1 infinity −0.054 2 stop infinity 0.0543 Lens 1 0.876 (ASP) 0.358 plastic 1.544 56.000 1.602 4 −37.188 (ASP)0.211 5 Lens 2 −0.412 (ASP) 0.213 plastic 1.651 21.500 7.268 6 −0.453(ASP) 0.030 7 Lens 3 0.626 (ASP) 0.254 plastic 1.651 21.500 3.216 80.764 (ASP) 0.333 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10infinity 0.131 11 Image infinity 0.000 plane

TABLE 6 Aspheric Coefficients surface 3 4 5 K: 1.1143E−01 4.5584E+03−5.0524E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −2.6472E−01−4.3381E−01 3.0370E+00 C: 2.4231E+00 1.0284E+01 −1.0318E+01 D:−3.2150E+01 −1.4021E+02 −1.4086E+01 E: 1.7801E+02 9.7852E+02 8.8790E+02F: −6.4089E+02 −3.3473E+03 −4.0655E+03 G 8.4568E+02 4.1659E+035.7099E+03 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K:−1.4714E+00 −1.2397E+01 −6.4401E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00B: −4.9828E−01 2.6913E+00 −4.5859E−01 C: 6.5987E+00 −2.3621E+015.1313E+00 D: −7.6651E+01 1.2891E+02 −3.6777E+01 E: 4.6447E+02−4.6825E+02 1.1797E+02 F: −1.0766E+03 9.5965E+02 −1.9549E+02 G8.5055E+02 −8.6698E+02 1.2566E+02 H 0.0000E+00 0.0000E+00 0.0000E+00

In the third embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the third embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 5 and Table 6 asthe following values and satisfy the following conditions:

Embodiment 3 f 1.076 f12/f3 0.50896 Fno 1.6 R2/R3 90.34390 FOV 65CT1/T12 1.69914 f1/f2 0.22035 T12/CT2 0.98882 f2/f3 2.26020 T12/T237.01767 f1/f3 0.49804 V1 − V2 34.5 f1/f23 0.84401 V1 − V3 34.5

Referring to FIGS. 4A and 4B, FIG. 4A shows a three-piece infraredsingle wavelength lens system in accordance with a fourth embodiment ofthe present invention, and FIG. 4B shows, in order from left to right,the longitudinal spherical aberration curves, the astigmatic fieldcurves, and the distortion curve of the fourth embodiment of the presentinvention. A three-piece infrared single wavelength lens system inaccordance with the fourth embodiment of the present invention comprisesa stop 400 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 410, a second lenselement 420, a third lens element 430, an IR cut filter 470, and animage plane 480, wherein the three-piece infrared single wavelength lenssystem has a total of three lens elements with refractive power. Thestop 400 is disposed between an image-side surface 412 of the first lenselement 410 and an object to be imaged.

The first lens element 410 with a positive refractive power has anobject-side surface 411 being convex near an optical axis 490 and theimage-side surface 412 being convex near the optical axis 490, theobject-side surface 411 and the image-side surface 412 are aspheric, andthe first lens element 410 is made of plastic material.

The second lens element 420 with a positive refractive power has anobject-side surface 421 being concave near the optical axis 490 and animage-side surface 422 being convex near the optical axis 490, theobject-side surface 421 and the image-side surface 422 are aspheric, andthe second lens element 420 is made of plastic material.

The third lens element 430 with a positive refractive power has anobject-side surface 431 being convex near the optical axis 490 and animage-side surface 432 being concave near the optical axis 490, theobject-side surface 431 and the image-side surface 432 are aspheric, andthe third lens element 430 is made of plastic material.

The IR cut filter 470 made of glass is located between the third lenselement 430 and the image plane 480 and has no influence on the focallength of the three-piece infrared single wavelength lens system.

The detailed optical data of the fourth embodiment is shown in table 7,and the aspheric surface data is shown in table 8.

TABLE 7 Embodiment 4 f(focal length) = 1.11 mm, Fno = 1.4, FOV = 64 deg.Curvature surface Radius Thickness Material Index Abbe # Focal length 0object infinity 500.000 1 infinity 0.000 2 stop infinity 0.000 3 Lens 10.848 (ASP) 0.364 plastic 1.544 56.000 1.508 4 −13.555 (ASP) 0.173 5Lens 2 −0.416 (ASP) 0.234 plastic 1.635 23.900 5.081 6 −0.445 (ASP)0.030 7 Lens 3 0.612 (ASP) 0.236 plastic 1.635 23.900 6.070 8 0.625(ASP) 0.358 9 IR-filter infinity 0.210 glass 1.517 64.167 — 10 infinity0.131 11 Image infinity 0.000 plane

TABLE 8 Aspheric coefficients surface 3 4 5 K: −6.8165E−02 −6.6204E+01−5.5086E−01 A: 0.0000E+00 0.0000E+00 0.0000E+00 B: −9.2855E−02−3.9781E−01 2.8075E+00 C: −1.7300E+00 −9.5082E−01 −1.4380E+01 D:−1.1434E+01 7.3878E+00 1.3482E+02 E: 3.1050E+02 2.2340E+00 −3.5346E+02F: −2.3349E+03 −1.6160E+02 3.2516E+02 G 5.0324E+03 3.4273E+02−1.3212E+01 H 0.0000E+00 0.0000E+00 0.0000E+00 surface 6 7 8 K:−1.6842E+00 −1.0036E+01 −6.3872E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00B: −4.2370E−01 2.1256E+00 −2.1000E−01 C: 2.6819E+00 −2.0101E+015.4441E−01 D: 8.1475E+00 1.1789E+02 −5.4072E+00 E: −8.0008E+01−4.9289E+02 −5.1579E+00 F: 4.9479E+02 1.1501E+03 3.0434E+01 G−8.8479E+02 −1.2123E+03 −2.9698E+01 H 0.0000E+00 0.0000E+00 0.0000E+00

In the fourth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fourth embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 7 and Table 8 asthe following values and satisfy the following conditions:

Embodiment 4 f 1.11 f12/f3 0.24379 Fno 1.4 R2/R3 32.60571 FOV 64 CT1/T122.10076 f1/f2 0.29673 T12/CT2 0.74124 f2/f3 0.83702 T12/T23 5.77300f1/f3 0.24837 V1 − V2 32.1 f1/f23 0.63936 V1 − V3 32.1

In the present three-piece infrared single wavelength lens system, thelens elements can be made of plastic or glass. If the lens elements aremade of plastic, the cost will be effectively reduced. If the lenselements are made of glass, there is more freedom in distributing therefractive power of the three-piece infrared single wavelength lenssystem. Plastic lens elements can have aspheric surfaces, which allowmore design parameter freedom (than spherical surfaces), so as to reducethe aberration and the number of the lens elements, as well as the totaltrack length of the three-piece infrared single wavelength lens system.

In the present three-piece infrared single wavelength lens system, ifthe object-side or the image-side surface of the lens elements withrefractive power is convex and the location of the convex surface is notdefined, the object-side or the image-side surface of the lens elementsnear the optical axis is convex. If the object-side or the image-sidesurface of the lens elements is concave and the location of the concavesurface is not defined, the object-side or the image-side surface of thelens elements near the optical axis is concave.

The three-piece infrared single wavelength lens system of the presentinvention can be used in focusing optical systems and can obtain betterimage quality. The three-piece infrared single wavelength lens system ofthe present invention can also be used in electronic imaging systems,such as, 3D image capturing, digital camera, mobile device, digital flatpanel or vehicle camera.

While we have shown and described various embodiments in accordance withthe present invention, it should be clear to those skilled in the artthat further embodiments may be made without departing from the scope ofthe present invention.

What is claimed is:
 1. A three-piece infrared single wavelength lenssystem, in order from an object side to an image side, comprising: astop; a first lens element with a positive refractive power, having anobject-side surface being convex near an optical axis and an image-sidesurface being convex near the optical axis, at least one of theobject-side surface and the image-side surface of the first lens elementbeing aspheric; a second lens element with a positive refractive power,having an object-side surface being concave near the optical axis and animage-side surface being convex near the optical axis, at least one ofthe object-side surface and the image-side surface of the second lenselement being aspheric; and a third lens element with a positiverefractive power, having an object-side surface being convex near theoptical axis and an image-side surface being concave near the opticalaxis, at least one of the object-side surface and the image-side surfaceof the third lens element being aspheric; wherein a focal length of thefirst lens element is f1, a focal length of the second lens element andthe third lens element combined is f23, and they satisfy the relation:0.5<f1/f23<0.71360; and wherein the lens system contains only three lenselements with refractive power.
 2. The three-piece infrared singlewavelength lens system as claimed in claim 1, wherein the focal lengthof the first lens element is f1, a focal length of the second lenselement is f2, and they satisfy the relation: 0.05<f1/f2<0.45.
 3. Thethree-piece infrared single wavelength lens system as claimed in claim1, wherein a focal length of the second lens element is f2, a focallength of the third lens element is f3, and they satisfy the relation:0.5<f2/f3<2.6.
 4. The three-piece infrared single wavelength lens systemas claimed in claim 1, wherein the focal length of the first lenselement is f1, a focal length of the third lens element is f3, and theysatisfy the relation: 0.05<f1/f3<0.7.
 5. The three-piece infrared singlewavelength lens system as claimed in claim 1, wherein a focal length ofthe first lens element and the second lens element combined is f12, afocal length of the third lens element is f3, and they satisfy therelation: 0.1<f12/f3<0.65.
 6. The three-piece infrared single wavelengthlens system as claimed in claim 1, wherein a radius of curvature of theimage-side surface of the first lens element is R2, a radius ofcurvature of the object-side surface of the second lens element is R3,and they satisfy the relation: 25<R2/R3<270.
 7. The three-piece infraredsingle wavelength lens system as claimed in claim 1, wherein thethree-piece infrared single wavelength lens system has a maximum viewangle FOV, and it satisfies the relation: 45<FOV<75.
 8. The three-pieceinfrared single wavelength lens system as claimed in claim 1, wherein acentral thickness of the first lens element along the optical axis isCT1, a distance along the optical axis between the first lens elementand the second lens element is T12, and they satisfy the relation:1.4<CT1/T12<2.4.
 9. The three-piece infrared single wavelength lenssystem as claimed in claim 1, wherein a distance along the optical axisbetween the first lens element and the second lens element is T12, acentral thickness of the second lens element along the optical axis isCT2, and they satisfy the relation: 0.5<T12/CT2<1.4.
 10. The three-pieceinfrared single wavelength lens system as claimed in claim 1, wherein adistance along the optical axis between the first lens element and thesecond lens element is T12, a distance along the optical axis betweenthe second lens element and the third lens element is T23, and theysatisfy the relation: 5.4<T12/T23<9.0.
 11. The three-piece infraredsingle wavelength lens system as claimed in claim 1, wherein an Abbenumber of the first lens element is V1, an Abbe number of the secondlens element is V2, and they satisfy the relation: 30<V1−V2<42.
 12. Thethree-piece infrared single wavelength lens system as claimed in claim1, wherein an Abbe number of the first lens element is V1, an Abbenumber of the third lens element is V3, and they satisfy the relation:30<V1−V3<42.
 13. The three-piece infrared single wavelength lens systemas claimed in claim 1, wherein a f-number of the three-piece infraredsingle wavelength lens system is Fno, and it satisfies the relation:1.2<Fno<1.8.